I'm also seeing this issue, also on a Debian Linux 4.19 kernel (on
updated Debian unstable VM), also on KVM, straight after rebooting the
VM. But without any suspending involved, I just reboot the VM, and as
soon as I can log in after rebooting its showing 6+ days of uptime.

The uptime jumps *very* early in the boot sequence, at the point that
kvm-clock starts reporting, by many days in my case.

Of note, the KVM host here is pretty old (Ubuntu 14.04 LTS, on
3.13.0-164-generic kernel, and qemu-kvm 2.0.0+dfsg-2ubuntu1.44). It's
also naturally a fairly old CPU (Intel Xeon X3450).

So I wonder if part of the trigger is newer (4.19) kernels relying on
CPU/hypervisor features that older CPUs / older hypervisors do not
provide/initialise. And maybe reading an uninitialised value as a result.